1. Field of the Invention
This invention relates to musical string instruments with fretted fingerboards, and more specifically to an improved nut mechanism that incorporates a string length intonation adjustment means and a means for rigidly securing the strings in position in order to ensure tuning stability.
2. Existing Art
It is well known in the art that stringed musical instruments with fretted fingerboards require specific string length and string height adjustments at the bridge and at the nut fulcrum points in order for the instrument to play in tune, and also be comfortable to play. String intonation is the technique wherein the theoretical length of a string is elongated in order to compensate for the increase in pitch that naturally occurs due to an increase in a string's tension as it is deflected away from its resting position and towards the fingerboard for contact. This “compensation” allows the musical notes produced by varying a string's vibrating length at specific frets along the fingerboard to be in tune relative to each other.
Throughout most of the history of fretted string instrument manufacture, this compensation was only done at the bridge fulcrum point. During the final adjustment phase of instrument production, a luthier would pluck the string, and at a point located precisely half way between the nut and the bridge, the luthier would then lightly touch the string thereby producing the first harmonic of the open string, with that note being an octave above pitch of the open string. The luthier would then deflect the string to the twelfth fret, located precisely at one half of the string's theoretical length, and pluck it in order to produce the fretted octave note of the open string. He would then compare these harmonic octave notes and fretted octave notes repeatedly while adjusting the position of the string's bridge fulcrum point away from the nut until the harmonic and fretted notes of the string being adjusted were identical.
Unfortunately, this technique only works in regards to fretted notes. When one compares the relationship between an instrument's fretted notes, and its open string notes wherein a string is simply plucked and allowed to vibrate between its bridge and nut fulcrum points, the ideal theoretical relationship between open string frequencies and fretted string frequencies does not exist. This is because vibrating open strings are not deflected towards the fingerboard, and therefore they do not require any compensation. The open string notes will therefore be lower in frequency in relationship to the fretted notes than they should be. With this, if a player tunes his instrument to its open string notes, the only fretted note that will be in ideal relative tune with the open string's pitch will be the fretted note produced at the twelfth fret. The fretted notes above the twelfth fret will go progressively flat as you move towards the bridge, and the fretted notes below the twelfth fret will go progressively sharp as you move towards the nut. A means must be used to restore the ideal relationship between open string and fretted note frequencies.
In an attempt to correct this difficulty and allow both open stings notes and fretted notes to be in relative tune with each other, the idea of additionally compensating a string's length at the nut in order to restore the ideal ratio between open string and fretted note frequencies has found its way into the art. Non-adjustable examples of this concept can be found in U.S. Pat. No. 4,295,404, U.S. Pat. No. 6,156,962, and U.S. Pat. No. 6,433,264. An adjustable example of a compensated string nut can be found in U.S. Pat. No. 5,750,910.
Another notable and recent attempt to deal with these tuning issues is disclosed in U.S. Pat. No. 7,378,582 to Kinoshita (Kinoshita). Kinoshita discloses a uniform projection that spans across the entire front of the string nut assembly. While the Kinoshita projection may or may not improve the intonation features of the musical instrument, it fails to provide each string-nut fulcrum with a varying linear position in relation to each individual string. In other words, Kinoshita merely applies the same linear position to each instrument string, treating all the strings uniformly and thus fails to ensure the ideal tuning of each string.
Furthermore, additional difficulties in keeping the instrument in proper tune arise with the usage of vibrato mechanisms. These mechanisms allow the player to vary the tension of the strings during play in order to produce a wide range of frequency related effects, most notably vibrato, which is a periodic change in a string's frequency. These mechanisms are difficult to use in that the return of a string to its original tension is very difficult to achieve because these mechanisms typically use springs for their restoring force. Changes in temperature, friction of a string's contact points at the bridge and nut, the stability of a string's material, and variations in the holding position of a string's tuning mechanism as a string's tension changes during vibrato mechanism usage all combine to make the tuning and stability of string tensions during play very difficult to achieve.
There are a variety of mechanisms within the art that provide the player with a means for eliminating string slippage at the nut in order to improve the tuning stability of the instrument. With each mechanism, the player rigidly secures a length of each string between two flat surfaces. U.S. Pat. No. 4,517,874, U.S. Pat. No. Des. 280,330, and U.S. Pat. No. 4,475,432 show string-locking mechanisms that require the usage of an allen wrench to secure the string between two flat surfaces. U.S. Pat. No. 4,574,678, U.S. Pat. No. 4,667,561, U.S. Pat. No. 4,669,350, U.S. Pat. No. 5,932,822, and U.S. Pat. No. Re. 32,863 each illustrate string-locking mechanisms that can be engaged manually by the player without the need for using a tool. Any of these locking mechanisms can be used with the present invention.